The invention relates to an electrical connection device for fastening to an electrically conductive structure and for being electrically connected to an electric cable. An application of the invention may lie with interconnecting electrical return circuits, in particular on board aircraft.
In modern aircraft, more and more metal structures are being replaced by carbon and/or composite structures, in particular in the fuselage. In the past, the metal structures of aircraft provided the functional electrical return for electrical equipment by grounding the equipment, enabled the conductive housings of electrical equipment to be bonded, enabled all of the non-electrical metal parts to be set to the same potential, provided electromagnetic compatibility (EMC) protection for electrical installations, and served to convey direct or indirect currents due to lightning.
The structures made of carbon and/or composite materials that now replace metal structures present low electrical conductivity and are poor at withstanding heating produced by Joule effects. It thus becomes necessary in modern aircraft to provide a specific return circuit for electronic equipment, which circuit is made up of independent conductors that are electrically interconnected (e.g. conductive bars, strips, and/or cables). Such an additional return circuit is referred to as an all equipotential electrical network (ALEEN). Electrically interconnecting equipotential conductor elements of primary, secondary, and ALEEN networks then serves to form the equipotential electrical network of the aircraft.
It is known, in particular in the context of ALEEN networks, to couple electrical braids and/or cables electrically to electrically conductive structures by means of terminal lugs. In the present application, the term “electric cable” is used broadly to designate any electrical conductor capable of forming part of a wired electrical network.
FIG. 1 shows an example of an electrical connection device 100 commonly used in aircraft. An electric cable 10 is crimped in a terminal lug 11. The terminal lug 11 presents an annular conductive surface 12 that is to be held in contact with any electrically conductive structure 13, e.g. a metal surface of the aircraft. The surface of the structure 13 is protected by an insulating layer, with the exception of a surface that is made to be conductive. The surface that is to be made conductive is for coming into electrical contact with the bottom pad of the conductive surface 12 of the terminal lug 11. This electrical contact is held and/or locked by assembly means comprising a stud 14 (e.g. having a screw thread) passing perpendicularly through the electrically conductive structure 13, washers 16, and a nut 15. For the above-described assembly, the electric cable 10 and the terminal lug 11 lie in a common plane that is parallel to the plane of the electrically conductive structure 13 or that is inclined at about 15° relative thereto.
Nevertheless, making that type of electrical connection requires a relatively large number of operations: preparing the surface by removing the insulating surface from the structure 13 facing the bottom pad of the terminal lug 11, with such removable revealing the electrically conductive surface so as to guarantee good electrical conductivity, applying a varnish so as to guarantee good sealing of the contact zone between the terminal lug 11 and the surface that has been made electrically conductive, putting into place the bottom pad of the terminal lug 11 around the stud 14 passing through the electrically conductive structure 13, followed by the washer(s) 16, and then by the nut 15. That type of assembly also requires an appropriate tightening torque to be applied. Specifically, if the torque is not sufficient, then the quality of the electrical contact between the terminal lug 11 and the electrically conductive structure 13, which is coupled to the vibration of the aircraft, will lead to an increase in contact electrical resistance, leading to an undesired rise in temperature. Conversely, if the clamping is excessive, there is then a risk of the conductive material suffering creep, which is harmful to the quality of the electrical contact. Properly controlling the clamping torque requires special attention since the drawbacks that are associated therewith are generally not visible while the terminal lug 11 is being assembled, and they become apparent only later.
Furthermore, during assembly or maintenance of electrical connections, there is a risk of electrically conductive foreign bodies (e.g. assembly tools, screws, nuts) dropping, being lost, or forgotten in the aircraft. This risk can lead to two different electrical polarities being put into contact, thereby giving rise to a short circuit and an electric arc. Mitigating this risk therefore implies performing additional mandatory tasks, such as inspecting and regularly cleaning zones of the aircraft that are at risk. At present, making the above-described electrical connection involves significant preparation, assembly, measurement, and maintenance times.